WO1984002856A1

WO1984002856A1 - Venturi washer for dust laden gas

Info

Publication number: WO1984002856A1
Application number: PCT/DE1984/000013
Authority: WO
Inventors: Wolfgang H Adlhoch; Johannes Lambertz
Original assignee: Rheinische Braunkohlenw Ag
Priority date: 1983-01-22
Filing date: 1984-01-19
Publication date: 1984-08-02
Also published as: AU2432784A; SE8404603D0; FI843275A0; FI79949C; SE8404603L; DE3490020C1; DE3490020D2; FI79949B; SE454408B; AU561189B2; CA1213513A; ZA84437B; FI843275A; US4578226A; DE3302148A1; GR79190B

Abstract

Venturi washer for dust laden gas with an inlet part (1) of which the channel (8) traversed by the gas narrows constantly in the flow direction (5, 6) and with an annular channel (13) for a liquid provided at the end of the larger diameter (12) of the inner part (1), which is connected throughout its periphery to the channel (13) of the inlet part (1) traversed by the gas, at least one liquid supply conduit (17) opening tangentially into the annular channel (13). The annular channel (13) is connected under overpressure conditions through a passage slot (27) to the channel (8) of the inlet part (1) traversed by the gas. The shape and the arrangement of said passage slot (27) are such that the liquid comes out parallel to the area which follows the wall (7) of the channel (8) along said wall. Thereby, a flow of a thin and uniform liquid film is obtained on the wall (7) of the channel (8), which film prevents solid particles from adhering to the wall (7).

Description

Venturi ashtray for dust-laden gases

The invention relates to a Venturi scrubber for staubbe¬ overloaded, flowing gases with an inlet part of which flowed through by the gas duct has a steadily decreasing in the direction of flow cross-section, and a maximum near the end diameter of E ^'inlau partly arranged ring channel for a liquid, the above its entire circumference is connected to the channel of the inlet part through which the gas flows, at least one feed line for the liquid opening into the annular channel in such a way that the latter flows into the annular channel with a tangential component.

Venturi washers of this type generally consist of three parts, namely the inlet part, the middle part and the diffuser. Due to the decreasing cross section of the inlet part in the flow direction, the velocity of the inflowing gas increases. The wall of this inlet part is modeled on a Venturi tube or, for the sake of simplicity, has a conical shape on the inside. The middle part adjoining the inlet part has the narrowest cross section, so that the gas velocity is greatest here. At this point, a liquid, usually water, is injected into the free cross-section of the central part, which is broken up into fine droplets by the rapidly flowing gas stream and carried away. In particular due to the speed difference between the liquid droplets and the solid particles to be removed in the gas stream, the solid particles hit the water droplets low. The flow of the gas slows down again in the diffuser-shaped extension behind the middle section. The pressure drop occurring when flowing through the narrowest point is partially recovered. The gas-water-solid mixture is then passed through a suitable apparatus, e.g. B. a cyclone, within which the dust-laden water droplets are separated from the gas stream, so that a gas with the desired purity is obtained. The water used to deposit the dust can be recycled several times. The dust is separated from the water in a sedimentation basin.

The injection of the water required for the separation of the solid particles takes place - viewed in the direction of flow - generally at the beginning of the narrowest cross section present in the middle part. The gas speed is highest here, so that the water supplied is accordingly broken up into particularly fine droplets.

Difficulties often arise from the fact that solid particles are deposited on the inner wall of the venturi washer, particularly in the inlet part, in the direction of flow before the point at which the water is injected. The resulting deposits grow counter to the direction of flow of the gas, whereby they can reach a size and extent that the flow conditions in the entire system are changed. In extreme cases, the Venturi washer can become completely blocked. In order to avoid the deposits and the resulting difficulties, it is already known from US Pat. No. 2,684,836 to provide an annular channel on a vertically arranged venturi washer in the area of the largest diameter of the inlet part, from which several pipe sections running in the circumferential direction originate, from which a liquid -

O PI speed, usually water, enter the inlet part under a certain pressure in such a way that its inner wall is covered with a liquid layer, which is intended to prevent deposits of solid particles. With this device, however, there is no guarantee that the liquid will be distributed evenly over the inner surface of the inlet part. Rather, there would be areas at the end of the largest diameter of the inlet part that are not wetted by the liquid. A liquid film covering the entire wall only appears in the lower region of the inlet part, but there is no guarantee that this liquid film will be reasonably uniform, at least with regard to its thickness and flow rate. For this reason, the feed pipe for the gas to be washed is led far into the inlet part in order to avoid that the incoming gas hits parts of the wall of the inlet part that are not sufficiently wetted. As a result, the axial length of the venturi washer is increased considerably. Another major disadvantage is that the liquid has only a low kinetic energy and thus has only a low rinsing effect. This is essentially due to the fact that the liquid enters the interior of the inlet part in a concentrated manner at a few points. Too high a pressure must be avoided, since otherwise there is a risk of turbulence forming and detaching particles from the liquid flow, which get into the free cross section of the inlet part and cause caking on the feed pipe there. With a slight overpressure, however, the flushing effect is not sufficient, since the liquid loses its swirl on the inner wall of the inlet part after a relatively short distance and only flows downward under the influence of gravity. The resulting flow velocity is too low for deposits to be avoided with certainty. in the Otherwise, the known device should be limited to a vertical arrangement of the venturi washer, since in the other case the aforementioned disadvantages have an even greater effect.

US Pat. No. 3,601,374 discloses a likewise vertically arranged venturi washer, the inlet part of which is provided at the end of the largest diameter with an annular channel for a liquid which is connected over its entire circumference to the channel of the inlet part through which the gas flows. Two feed lines for the liquid flow tangentially into the ring channel. The latter is merely an extension of the inlet part. It is completely open on its side facing the inside of the inlet part, so that the liquid moving in the circumferential direction in the ring channel under the action of gravity has an edge which separates the ring channel from the inner wall of the inlet part , flows into the latter. Here, too, it applies that the flow velocity of the liquid, which essentially only comes about under the influence of gravity, is insufficient. Avoid caking. A better flushing effect could only be achieved by increasing the amount of flushing water and thus a thicker layer of water on the inner wall of the inlet part. However, this leads to higher water consumption. In fact, the liquid supplied to this known device via the ring channel is to be taken up in finely divided form by the gas stream in order to bind the solid particles therein.

The object of the invention is to design a Venturi washer of the type described in the introduction in such a way that the disadvantages of known devices do not occur. In particular, permanent deposits should be reliably avoided with economical liquid consumption, even with fluctuating gas quantities and fluctuating quantities solid items inside. Furthermore, the venturi washer should be usable regardless of whether it is arranged vertically or horizontally or in any intermediate position. The shortest possible overall length is also sought. The structure of the venturi washer should be simple and clear.

To achieve this object, the invention proposes that the pressurized annular channel be connected via a passage gap to the channel through which the gas flows and the passage gap is directed towards the end of the smallest diameter of the inlet part. This configuration ensures that the liquid exits the channel over the entire circumferential surface of the flow channel located within the inlet part for the gas to be cleaned and, because of the tangential feed into the ring channel, also a certain swirl, i.e. one in the circumferential direction of the inner wall of the inlet part directional speed component, but at the same time also receives an axial component, the speed, in particular also in the axial direction, being adjustable by the pressure conditions within the ring channel. A liquid film emerges from the passage gap, which is coherently uniform over the entire circumference and extends over the entire length of the inlet part over all areas of the wall of the channel through which the gas flows. The solid particles adhering to the inner wall of the inlet part are flushed away by the flow energy of the liquid, so that a thin liquid film can be used which, since it already exits the passage gap in the flow direction of the gas, can be used , shows no turbulence or irregularities. The latter is achieved in a particularly advantageous manner if the passage gap is arranged in a direction essentially parallel to the adjacent area of the inner wall of the inlet part.

is not. The arrangement is advantageously such that the passage gap is delimited on the outside by the inner wall of the inlet part, so that the liquid film already within the passage gap with the inner wall delimiting the channel, along which it should flow towards the end of the smallest diameter of the inlet part. is in close contact.

In order to achieve a simple and reliable construction, the ring channel and passage gap are advantageously delimited by a ring which can be screwed axially into the inlet part. This type of configuration also gives the possibility of simply adjusting the width of the passage gap. For this purpose, the ring is screwed more or less deeply into the thread on the inlet part according to the respective operating conditions. Different operating conditions exist, for example, with different gas quantities and with different dusts, both with regard to the grain size and with regard to the type of dusts and also with regard to the respective states of the gas with regard to pressure, temperature and flow rate. For washing gas generated, for example, in a Winkler gasifier by gasifying lignite, it has proven to be expedient to set the passage gap to a width between 0.1 and 1 mm, preferably to about 0.5 mm.

An embodiment has proven to be particularly advantageous in which the passage gap is limited by the area of the smallest outside diameter of the ring and the area of the largest inside diameter of the inlet part. It is readily possible for the two wall regions of the ring, on the one hand, and the inlet part, on the other hand, which delimit the passage gap on its outlet side, to run essentially parallel to one another.

This also helps to let the liquid emerge from the passage gap evenly and without significant turbulence, so that the liquid film covering the inner wall of the channel through which the gas flows is also uniform and can therefore be thin, but covers the entire inner wall of the channel.

According to a further proposal of the invention, the smallest diameter of the inner cross-section of the ring through which the gas flows can be somewhat smaller than the largest diameter of the wall of the channel through which the gas flows through. It is expedient for the inner cross section of the ring through which the gas flows to have a diameter which decreases continuously in the direction of flow. With this arrangement, the gas flows through the ring into the channel of the actual inlet part. Due to the narrowing inner diameter of the ring in the flow direction, the gas flow experiences a first, locally limited acceleration. As a result, the flow profile of the gas flow is influenced in such a way that the boundary layer which otherwise occurs in the vicinity of the wall and which may move against the actual flow direction is interrupted. Since the usual, generally laminar boundary layer also favors the deposition of solid particles and thus the formation of caking, the embodiment according to the invention helps to prevent deposits in the direction of flow before the passage gap.

In the drawing, an embodiment of the invention is shown. Show it:

1 shows a venturi washer in longitudinal section, FIG. 2 shows the inlet part of the venturi washer in longitudinal section on a larger scale,

Fig. 3 is a front view of the inlet part in

4, in longitudinal section, the ring delimiting the passage gap on a larger scale.

The venturi washer shown in the drawing consists of an inlet part 1, a middle part 2 and a diffuser 3. This order of the parts corresponds to ^* the direction of flow of the gas which flows into the washer in the direction of arrow 5 and this in the direction of arrow 6 leaves again.

The inner wall 7 of the inlet part 1 delimits a channel 8 which tapers continuously in the flow direction 5, 6. The middle part 2 has the smallest flow cross section. Immediately in front of this are radial bores 9, through which a liquid detergent, generally water, is introduced into the cross section of the central part 2 through which the gas flows. The water is supplied via a pipe connection 10.

In the flow direction behind the middle part 2, there is the diffuser 3, the wall 11 of which continuously widens in the flow direction. In the narrowest point of the middle part 2, the gas reaches its highest flow rate, which in the diffuser 3 decreases again according to the cross-sectional enlargement thereof to a value which corresponds approximately to the speed at which the gas enters the inlet part.

The unavoidable deposits and caking occur if no special precautions are taken ^'in the flow direction 5, 6 short of the region on which the through holes 9, the washing liquid into the Innen¬ cross-section of the central part 2 occurs. These deposits

OMPI grow along the wall 7 of the channel 8 against the flow direction 5, 6 and also into the inlet part 1, as a result of which the flow conditions change and at least the operation of the venturi washer is severely impaired.

To avoid these difficulties, an annular channel 13 is provided near the end 12 of the largest cross section of the inlet part 1 and extends with its outer circumference into the fastening flange 14. On the inside, the ring channel 13 is delimited by a ring 15 which is screwed axially into the inlet part 1 or the flange 14 via a fine thread 16. At least two supply channels 17 for a liquid, preferably water, approximately tangentially open into the outer circumference of the ring channel, so that the liquid within the ring channel has a large movement component in the circumferential direction thereof.

The ring 15 which delimits the ring channel on the inside consists of a ring body which has a fine thread 16 on its outer circumference. Furthermore, small bores 20 are provided for the engagement of a tool with which the ring 15 can be screwed into the inlet part 1. The front end 21 opposite to the flow direction 5, 6 merges via a region 22 rounded off with a large radius 23 into a conical surface 24, the inclination angle of which, for. B. is 15 ° and advantageously corresponds to the angle of inclination at least of the adjoining region of the wall 7 of the channel 8. By adapting the inflow cross sections over conical surfaces of the same inclination, flow conditions for the gas are achieved in the inlet part 1 which are free or at least almost free of turbulence.

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_ OMPI At its area facing the middle part 2, the outer circumferential surface 25 of the ring 15 is provided with a diameter that decreases in the flow direction in such a way that it is rounded convexly in longitudinal section over a large radius 26. The area of the circumferential surface 25 facing the cylindrical or threaded part 16 of the ring 15 serves as an inner boundary of the ring channel 13, which merges into a passage gap 27 at its area facing the rear end face or edge 19 of the ring 15. The latter is limited on the outside by the area of greatest diameter of the wall 7 of the channel 8. Through this entrance slit 27, the liquid, and in the form of a thin liquid film of the Wandun g ^'7 of the channel 8 enters covered in the channel 8 of the inlet portion. 1 The area of the lateral surface 25 facing the end face 19 runs approximately parallel to the opposite area of the wall 7 of the channel 8, so that the liquid emerging from the passage gap 27 has a movement component which runs approximately parallel to the longitudinal course of the wall 7 and which leads to a uniform flow and distribution of the resulting liquid film, which rotates along the wall 8 and at the same time moves in the direction of the central part 2.

The water emerging from the passage gap 27 under a certain excess pressure and at a relatively high speed flushes away solid particles which have been deposited on the wall 7 of the channel 8, so that caking is avoided with certainty.

The width of the annular gap can be, for example, 0.5 mm with a diameter of 70 mm. Here, 100 1 / min. Water is required to form the liquid film flowing along the wall 7 of the channel 8, about 300 1 / min. given for washing the gas in the middle part 2 become. The inlet part has z. B. an axial length of 110 mm and a largest and a smallest cross section of 70 and 23 mm. The amount of gas washed can, on average, e.g.

3 B. in the order of 5 m / min. lie.

The wall 7 has a cone angle of the order of 10 °. The inlet part 1 can also be designed such that the region facing its end with the largest diameter 12 has an angle of approximately 15 °. This possibility is shown in FIG. 1 of the drawing.

Due to the fact that the liquid film on the wall 7 is very thin and uniform, it is not torn apart either by the gas flowing in the channel 8 or by the dust particles carried along. Rather, it helps to significantly reduce the friction between the gas and the wall 7, so that a lower pressure loss of the gas occurs.

Claims

EXPECTATIONS

1. Venturi washer for dust-laden, flowing gases with an inlet part, the channel through which the gas flows has a continuously decreasing cross-section in the direction of flow, and a near the end of the largest diameter of the inlet part arranged annular channel for a liquid, which over its entire circumference with the Gas flow channel of the inlet part is connected, wherein at least one feed line for the liquid opens into the ring channel such that the latter flows into the ring channel with a tangential component, characterized in that the ring channel (13) which is under pressure Via a passage gap (27) is connected to the channel (8) through which the gas flows and the passage gap (27) is directed towards the end of the smallest diameter of the inlet part (1).

2. Venturi washer according to claim 1, characterized in that the wall (7) of the inlet part forms one of the limits of the passage gap (27).

3. Venturi washer according to claim 1 or 2, characterized gekenn¬ characterized in that the passage gap (27) is arranged substantially parallel to the adjacent region of the wall (7) of the gas flow channel (8) directed.

4. Venturi washer according to claim 1 or 2, characterized gekenn¬ characterized in that the annular channel (13) and passage gap (27) by an axially in the inlet part (1) screwable ring (15) are limited.

5. Venturi washer according to claim 4, characterized in that the passage gap (27) is adjustable in terms of its width.

OMPI \

6. Venturi washer according to claim 4, characterized in that the passage gap (27) from the area of smallest outer diameter of the ring (15) and the area of largest inner diameter of the inlet part (1) is limited.

7. Venturi washer according to one of the preceding claims, characterized in that the two wall regions of the ring (15) delimiting the passage gap (27) on the one hand and the inlet part (1) on the other hand run essentially parallel to one another.

8. Venturi washer according to one of the preceding claims, characterized in that the smallest diameter of the inner cross section of the ring through which the gas flows is somewhat smaller than the largest diameter of the channel (8) through which the gas flows in the inlet part (1).

9. Venturi washer according to one of the preceding claims, characterized in that the inner cross-section of the ring (15) through which the gas flows has a diameter which decreases continuously in the direction of flow.

10. Venturi washer according to one of the preceding claims, characterized in that the area of the narrowest diameter of the inlet part (1) facing section of the ring (15) on the outside has a continuously tapered outer surface which has the annular channel (13) and the passage gap (27) limited.

OMPI

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